1. Field of the Invention
The present invention relates to a horizontal-type biaxial kneader used for such operation as kneading rubber and, more particularly, to a horizontal-type biaxial kneader having characters in the cross-sectional configuration of rotor blades.
2. Description of the Prior Art
Conventionally, an intensive mixer (banbury type) or a horizontal-type biaxial internal kneader equipped with rotor blades having a cross-sectional configuration like a convex lens or a circle with an angular portion has been employed for such operation as kneading rubber and adding compounds.
The effect of kneading rubber by rotor blades has already been confirmed mainly by the above-mentioned banbury mixer representative of rubber kneaders. However, it has not been clear yet how the rubber kneading effect of the rotor blades is influenced by the cross-sectional configuration and size of each rotor blade, and factors of the cross-sectional configuration (for example, a tip clearance, a land width, a bite angle on the front side of the tip of the rotor blade, i.e., a front angle between the rotor blade and the chamber wall).
Besides, few attempts have been made to research changes of the mixing behavior of rubber in an interposed region below a ram and above a bridge between two rotor blades when the cross-sectional configuration of the rotor blades is different. Instead of two-dimensional mixing behavior on a cross-section of such an apparatus, three-dimensional mixing behavior in the whole apparatus has been investigated. This is because the mixing behavior of rubber in the interposed region below the ram and above the bridge varies at every rotation of the rotor blades and is highly complicated. The reason is that the rotor blades are helically deformed in the axial direction although they have one common shape, and that the two rotor blades of the internal mixer are rotated at a speed ratio of approximately 1:1.2, so that the phase difference is changed with rotations.
In a conventional horizontal-type biaxial internal kneader represented by the banbury mixer, the rotor blades have a phase difference shown in FIG. 10 only once per rotation of the rotor blades, and the number of interchanges of the content between the rotor blades is small. Further, in a rotor blade having a cross-sectional configuration shown in FIG. 12, a scrape angle on the rear side of the tip of the rotor blade, i.e., a rear angle between the rotor blade and the chamber wall, is small. The space between the rotor blade and the peripheral wall within the mixing chamber on the rear side of the rotor blade tip is narrow, and accordingly, the transfer/mixing space for the content is small. In practice, therefore, the attached content is not easily separated from the peripheral wall within the mixing chamber although a large negative pressure which is effective for separation of the content is generated on the rear side of the rotor blade tip, and mixing efficiency is extremely low. This factor inevitably results in the inconvenience that the conventional kneader has low mixing rate and unfavorable performance.
In a horizontal-type biaxial internal kneader whose rotor blades have a lens-like cross-sectional configuration, the rotor blades have a phase difference shown in FIG. 10 only once per rotation of the rotor blades, and the number of interchanges of the content between the rotor blades is small. Further, as shown in FIG. 11, the rear-side edge of each rotor blade has a convex shape. A scrape angle on the rear side of the tip of the rotor blade is large, and the space between the rotor blade and the peripheral wall within the mixing chamber on the rear side of the rotor blade tip is wide. Consequently, a negative pressure generated on the rear side of the rotor blade tip is small, and the transfer/mixing space for the content is not large enough although it is not so small as that of the above-described rotor blade having the cross-sectional configuration like a circle with an angular portion. Therefore, mixing efficiency is extremely low. This factor inevitably results in the inconvenience that this kneader has low mixing rate and unfavorable performance.
Concerning mixing operation involving scraping a highly viscous substance, the inventors of the present invention obtained a distribution of pressure generated on the front and rear sides of the tip of a scraper blade when a highly viscous fluid was scraped, through measurement of a normal stress distribution on a peripheral wall within a vessel. The result is shown in FIG. 8. Positive pressure (positive normal stress) was generated on the front side of the scraper blade tip, and negative pressure (negative normal stress) was generated on the rear side of the same. As a scrape angle .delta. on the rear side of the scraper blade tip became smaller, the negative pressure was more increased. The power consumption of the scraper blade was greatly influenced by the scrape angle .delta. on the rear side of the scraper blade tip, and it had the smallest value when the scrape angle .delta. was 45.degree.. Taking this matter into account, as shown in FIG. 9, the inventors speculated that the power consumption and the mixing efficiency are considerably influenced by the pressure on a peripheral wall within a mixing chamber which varies in accordance with a bite angle .gamma. on the front side of the tip of a rotor blade and a scrape angle .delta. on the rear side of the same, and that a large positive pressure is generated when the bite angle .gamma. on the front side of the rotor blade tip is decreased, whereas a large negative pressure is generated when the scrape angle .delta. on the rear side of the rotor blade tip is decreased. Moreover, the inventors considered that, because such a large pressure difference is caused between the front and rear sides of the tip of each rotor blade, the pressure generated in a region below a ram and above a bridge significantly varies according to the positional relation (phase difference) between tips of two rotor blades when the tips of the rotating blades reach this region. Then, in order to improve the rotor blades, the inventors investigated the effect of the cross-sectional configuration of the rotor blades on rubber kneading when rotating the two rotor blades at equal speed in directions opposite to each other so as to maintain the positional relation between the rotor blade tips constantly under a certain condition.
The present invention has been achieved to solve the above-described problems, and it is an object of the invention to provide a horizontal-type biaxial kneader in which separation and mixing of the content on the rear side of each rotor blade can be favorably performed and the content can be effectively interchanged between two rotor blades through an interposed region below the ram and above the bridge between the blades.